Apparatus and method for high-speed synchronization in wireless communication

ABSTRACT

A method includes calculating first correlation values corresponding to a first symbol duration based on input samples, the input samples being generated from a received signal; calculating phase differences respectively corresponding to the input samples based on the first correlation values and second correlation values corresponding to a second symbol duration preceding the first symbol duration; updating accumulative phase differences respectively corresponding to the input samples based on the phase differences; and detecting a symbol boundary based on the updated accumulative phase differences.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to Korean PatentApplication No. 10-2021-0164866 and 10-2022-0030944, filed on Nov. 25,2021, and Mar. 11, 2022, in the Korean Intellectual Property Office, theentire disclosures of which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to wireless communication, and moreparticularly, to an apparatus and method for high-speed synchronizationin wireless communication.

Wireless network technologies include wireless local area network (WLAN)technology and wireless personal area network (WPAN) technology. A WLANis a group of locally located computers or other devices that form awireless network which is based on radio transmissions rather than wiredconnections. A WLAN may be based on an Institute of Electrical andElectronics Engineers (IEEE) 802.11 standard, and may be formed in aradius of about 100 m. A WPAN is a personal area wireless network thatinterconnect devices centered around an individual person's workplacebased on wireless connections. A WPAN may be based on the IEEE 802.15standard, and include Bluetooth, ZigBee, ultra-wide band (UWB), etc. Awireless network includes a plurality of communication devices, and thecommunication devices collect packets in real time and transmit packetsin an active period.

SUMMARY

A method includes calculating first correlation values corresponding toa first symbol duration based on input samples, the input samples beinggenerated from a received signal; calculating phase differencesrespectively corresponding to the input samples based on the firstcorrelation values and second correlation values corresponding to asecond symbol duration preceding the first symbol duration; updatingaccumulative phase differences respectively corresponding to the inputsamples based on the phase differences; and detecting a symbol boundarybased on the updated accumulative phase differences. An apparatusincludes a first buffer configured to store input samples generated froma received signal and corresponding to a first symbol duration; aprocessing circuit configured to calculate first correlation valuesrespectively corresponding to the input samples based on the inputsamples; a second buffer configured to store second correlation valuescorresponding to a second symbol duration preceding the first symbolduration; and a third buffer configured to store accumulative phasedifferences respectively corresponding to the input samples, wherein theprocessing circuit is further configured to: calculate phase differencesrespectively corresponding to the input samples, based on the firstcorrelation values and the second correlation values; update theaccumulative phase differences based on the phase differences; anddetect a symbol boundary based on the updated accumulative phasedifferences. An apparatus includes a memory storing a series ofinstructions; and at least one processor configured to, by executing theseries of instructions, calculate first correlation values correspondingto a first symbol duration and respectively corresponding to inputsamples, the input samples being generated from a received signal;calculate phase differences respectively corresponding to the inputsamples, based on the first correlation values and second correlationvalues corresponding to a second symbol duration preceding the firstsymbol duration; update accumulative phase differences respectivelycorresponding to the input samples based on the phase differences; anddetect a symbol boundary based on the updated accumulative phasedifferences. A method includes receiving a wireless signal from adevice; identifying input samples corresponding to a first symbolduration based on the wireless signal; calculating first correlationvalues respectively corresponding to the input samples; calculatingphase differences respectively corresponding to the input samples basedon the first correlation values and second correlation valuescorresponding to a second symbol duration preceding the first symbolduration; updating accumulative phase differences respectivelycorresponding to the input samples based on the phase differences;performing simultaneous time and frequency synchronization based on theupdated accumulative phase differences; and processing the wirelesssignal based on the simultaneous time and frequency synchronization.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will be more clearly understoodfrom the following detailed description taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a diagram illustrating a wireless network according to anembodiment;

FIG. 2 is a block diagram illustrating a wireless communication deviceaccording to an embodiment;

FIG. 3 is a diagram illustrating a physical (PHY) protocol data unit(PPDU) according to an embodiment;

FIGS. 4A to 4D are diagrams illustrating examples of PPDUs according toembodiments;

FIG. 5 is a diagram illustrating an example of a preamble symbolaccording to an embodiment;

FIG. 6 is a diagram illustrating an example of a preamble code accordingto an embodiment;

FIGS. 7A and 7B are diagrams illustrating preamble parameters accordingto embodiments;

FIG. 8 is a flowchart illustrating a method for high-speedsynchronization according to an embodiment;

FIG. 9 is a diagram illustrating an operation of calculating correlationvalues according to an embodiment;

FIG. 10 is a flowchart illustrating a method for high-speedsynchronization according to an embodiment;

FIG. 11 is a flowchart illustrating a method for high-speedsynchronization according to an embodiment;

FIG. 12 is a flowchart illustrating a method for high-speedsynchronization according to an embodiment;

FIG. 13 is a flowchart illustrating a method for high-speedsynchronization according to an embodiment;

FIG. 14 is a flowchart illustrating a method for high-speedsynchronization according to an embodiment;

FIG. 15 is a flowchart illustrating a method for high-speedsynchronization according to an embodiment;

FIGS. 16A and 16B are block diagrams illustrating examples ofsynchronizers according to embodiments; and

FIG. 17 is a block diagram illustrating a synchronizer according to anembodiment.

DETAILED DESCRIPTION

FIG. 1 is a diagram illustrating a wireless network 10 according to anembodiment. Specifically, FIG. 1 shows examples of device-to-device(D2D) communication in the wireless network 10.

As an example of the wireless network 10, a wireless personal areanetwork (WPAN) may be formed in a relatively short radius of about 10 m.As an example of a WPAN, ultra-wide band (UWB) may refer to acommunication technology, in a baseband, using a wide frequency bandequal to or greater than several GHz, low spectral density, and shortpulse width or a band to which or UWB communication is applied. The IEEE802.15.4 standard specifies a physical (PHY) layer and a medium accesscontrol (MAC) sublayer of UWB. The IEEE 802.15.4 standard defines highrate pulse repetition frequency UWB (HRP-UWB) and low rate pulserepetition frequency UWB (LRP-UWB), and recently IEEE 802.15.4z hasdefined higher pulse repetition frequency UWB (HPRF-UWB) in HRP-UWB. Thepresent disclosure uses UWB as an example of the wireless communicationtechnology used in the wireless network 10, but it is noted that thepresent disclosure is not necessarily limited to UWB and may be appliedto other wireless communication technologies.

Device-to-Device (D2D) communication may refer to a method in whichgeographically close wireless communication devices directly communicatewith each other without using an infrastructure, such as a base station.D2D communication may use an unlicensed frequency band, such as Wi-FiDirect and Bluetooth, or may improve the frequency use efficiency of acellular system by utilizing a licensed frequency band. In someembodiments of the present disclosure, D2D communication may refer tocommunication between wireless communication devices as well ascommunication between things or thing intelligent communication in theInternet of Things (IoT).

Referring to FIG. 1 , the wireless network 10 may include variouscommunication schemes. For example, as shown by a dashed-dotted line inFIG. 1 , one-to-one communication, in which one wireless communicationdevice communicates with one wireless communication device, may occur inthe wireless network 10. Also, as shown by a dashed line in FIG. 1 ,one-to-many communication, in which one wireless communication devicecommunicates with a plurality of wireless communication devices, mayoccur in the wireless network 10. Also, as shown by the solid line inFIG. 1 , many-to-many communication, in which a plurality of wirelesscommunication devices communicate with a plurality of wirelesscommunication devices, may occur in the wireless network 10. Thewireless communication device (i.e., a receiver) may obtainsynchronization based on a preamble of a signal received from anotherwireless communication device (i.e., a transmitter). A preamble is asignal used in network communications to synchronize transmission timingbetween two or more systems. In general, preamble is a synonym for“introduction.” The role of the preamble is to define a specific seriesof transmission criteria that make components such as transmitters andreceivers to known in advance that data is to be transmitted. Forexample, as will be described below with reference to FIG. 3 , thetransmitter may transmit a PHY protocol data unit (PPDU) including asynchronization header (SHR), and the SHR may have a structure known inadvance to the transmitter and the receiver. The receiver may performchannel estimation after completing synchronization of time andfrequency. When time required for synchronization increases in thereceiver, the accuracy of channel estimation may decrease, and thus,communication performance, such as positioning and throughput, maydeteriorate. In addition, when using more resources to reduce the timerequired for synchronization, the cost, such as chip size and powerconsumption, may increase and that may result in lower wirelesscommunication efficiency.

As will be described below with reference to the drawings, the wirelesscommunication device may include an apparatus that provides high-speedsynchronization, and accordingly, the time needed for the receiver tocomplete time and frequency synchronization may be reduced. For example,a coherent integration may be used for synchronization despite a carrierfrequency offset, and accordingly, the time needed for a symbol boundaryto be accurately detected may be reduced. In addition, the detection ofthe symbol boundary and the detection of the carrier frequency offsetmay be completed at the same time, and accordingly, resources requiredfor synchronization may be reduced. In addition, due to that the timefor synchronization may be reduced, the time for channel estimation maybe extended, and accordingly, the accuracy of channel estimation mayimprove, and communication performance may increase.

FIG. 2 is a block diagram illustrating a wireless communication device100 according to an embodiment. The wireless communication device 100may refer to a device that performs wireless communication in thewireless network 10 of FIG. 1 . For example, the wireless communicationdevice 100 may be a portable device, such as a mobile phone, a laptopPC, a tablet PC, etc., a stationary device, such as a desktop PC, asmart TV, a kiosk, etc., a vehicle, such as an automobile, personalmobility machine, etc., or a component included in the devices describedabove. As shown in FIG. 2 , the wireless communication device 100 mayinclude a processor 110, a transmit (TX) data path 120, adigital-to-analog converter (DAC) 130, a TX RF circuit 140, a TXantenna. 150, a receive (RX) antenna 160, an RX RF circuit 170, ananalog-to-digital converter (ADC) 180, and an RX data path 190. A radiofrequency (RF) circuit is a type of analog circuit operating at the highfrequencies suitable for wireless transmission. An RF circuit may useinductive elements to tune the resonant circuit operation around aspecific radio carrier frequency. In some embodiments, the components ofthe wireless communication device 100 may be embedded in one chip or maybe respectively embedded in two or more chips mounted on a printedcircuit board (PCB). In some embodiments, the TX data path 120 and theRX data path 190 may be embedded in one chip, and may be collectivelyreferred to as a modem. Also, in some embodiments, the DAC 130 and/orthe ADC 180 may be included in the modem.

The processor 110 may provide a PHY service data unit (PSDU) to the TXdata path 120 and may receive the PSDU from the RX data path 190. Theprocessor 110 may generate the PSDU from data to be transmitted toanother wireless communication device, and may provide the PSDU to theTX data path 120. In addition, the processor 110 may extract datatransmitted by another wireless communication device from the PSDUreceived from the RX data path 190. An example of the PSDU will bedescribed below with reference to FIG. 3 . In some embodiments, theprocessor 110 may execute an operating system (OS), and may execute atleast one application on the OS, and the PSDU may be generated orprocessed by the OS and/or the at least one application.

The TX data path 120 may receive the PSDU from the processor 110 and mayprovide a digital signal to the DAC 130. As shown in FIG. 2 , the TXdata path 120 may include an encoder 122, a modulator 124, and a TXfilter 126. The encoder 122 may encode the PSDU provided from theprocessor 110. For example, the encoder 122 may encode the PSDU based onReed-Solomon encoding, and add a PHY header (PHR) including single errorcorrect double error detect (SECDED) bits to the encoded PSDU. Theencoder 122 may use various encoding methods, including convolutionalencoding, and may insert the SHR after performing spreading. Themodulator 124 may generate a PPDU by modulating a signal provided fromthe encoder 122. For example, the modulator 124 may modulate the PHR,based on burst position modulation (BPM) and binary phase-shift keying(BPSK), and modulate the spread PSDU, i.e., a PHY payload, to a ratespecified in the PHR. The TX filter 126 may filter the PPDU providedfrom the modulator 124.

The DAC 130 may convert a digital signal output from the TX data path120 into an analog signal, and the TX RF circuit 140 may generate an RFsignal from the analog signal and may provide the RF signal to the TXantenna 150. In this example, an RF signal may be referred to as atransmitting signal. In some embodiments, the TX RF circuit 140 mayinclude an analog filter, an analog mixer, and/or a power amplifier.

The RX RF circuit 170 may generate an analog signal from the RF signalreceived from the RX antenna 160, and may provide the analog signal tothe ADC 180. In some embodiments, the RX RF circuit 170 may include ananalog filter, an analog mixer, and/or a low noise amplifier. The ADC180 may convert the analog signal provided from the RX RF circuit 170into a digital signal, and may provide the digital signal to the RX datapath 190. In some embodiments, the RX RF circuit 170 may extract anin-phase (I) signal and a quadrature (Q) signal from the RF signalreceived via the RX antenna 160, and the ADC 180 may provide I samplesand Q samples generated by sampling the I signal and the Q signal,respectively, to the RX data path 190.

The RX data path 190 may receive the digital signal from the ADC 180 andmay provide the PSDU to the processor 110. As shown in FIG. 2 , the RXdata path 190 may include an RX filter 192, a synchronizer 194, ademodulator 196, and a decoder 198. The RX filter 192 may filter thedigital signal provided from the ADC 180. The synchronizer 194 mayperform synchronization based on the digital signal provided by the RXfilter 192, and may provide a result of synchronization to the RX filter192. For example, the digital signal may include a series of samples andthe synchronizer 194 may perform time synchronization by detecting thesymbol boundary from input samples received from the RX filter 192. Inthis example, the sample may be referred to as input samples. Also, thesynchronizer 194 may perform frequency synchronization by detecting aninitial phase and a carrier frequency offset (CFO) of the input samples.In some embodiments, the input sample provided from the RX filter 192may include a sample corresponding to the I signal and a samplecorresponding to the Q signal.

The synchronizer 194 may provide information about the detected initialphase and carrier frequency offset to the RX filter 192, and the RXfilter 192 may provide the PPDU to the demodulator 196 by compensatingfor the phase and carrier frequency offset based on the informationprovided from the synchronizer 194. The synchronizer 194 may also informother components, such as the demodulator 196 and/or the decoder 198, ofthe completion of synchronization in the RX data path 190. Thedemodulator 196 may demodulate the PPDU received from the RX filter 192,and the decoder 198 may generate the PSDU by decoding the signalprovided from the demodulator 196 and provide the PSDU to the processor110. In some embodiments, the demodulator 196 and the decoder 198 mayperform operations corresponding to the modulator 124 and the encoder122 described above, respectively.

FIG. 3 is a diagram illustrating a PPDU according to an embodiment.Specifically, FIG. 3 shows the PPDU used in HRP-UWB. In someembodiments, the wireless communication device 100 of FIG. 2 maytransmit the PPDU to, or receive the PPDU from, another wirelesscommunication device.

Referring to FIG. 3 , the PPDU may include an SHR, a PHR, and a PHYpayload (or a PHY payload field). The SHR may include a code known inadvance to a transmitter and a receiver, and the receiver may performsynchronization and channel estimation based on the SHR and the code. Asshown in FIG. 3 , the SHR may include a SYNC field and a start of framedelimiter (SFD) field. The SYNC field may be referred to as a preambleand may include NSYNC repeated preamble symbols, which may be referredto as symbols herein. NSYNC may be known in advance to the transmitterand receiver. An example of a symbol included in the SYNC field will bedescribed below with reference to FIG. 5 . The SFD field may inform thatthe PHR starts after the SYNC field ends. The SFD field may be used tobuild frame timing. For example, in ranging, the time at which an SFD isdetected may be determined to be a packet frame transmission time and/ora packet frame reception time. In some embodiments, the SFD field mayinclude 8 or 16 symbols.

The PHR may include information for decoding the PHY payload. Forexample, the PHR may include information used for PSDU transmission,including information about a data rate, a preamble length, a PSDUlength, etc. In some embodiments, the PHR may include 16 symbols. TheMAC frame may include a MAC header (MHR), a MAC payload, and a MACfooter (MFR). The MAC frame may be transferred to the PHY as a PSDU,which is a PPDU payload.

FIGS. 4A to 4D are diagrams illustrating examples of PPDUs according toembodiments. Specifically, FIGS. 4A to 4D show examples of PPDU used inHPRF-UWB as defined in the IEEE 802.11.4z standard. In some embodiments,the wireless communication device 100 of FIG. 2 may transmit at leastone of the PPDUs of FIGS. 4A to 4D to or receive at least one of thePPDUs of FIGS. 4A to 4D from another wireless communication device. InFIGS. 4A to 4D, arrows may indicate reference positions.

HPRF-UWB defines four different modes according to a scrambled timestampsequence (STS) packet configuration. An STS may include a code encryptedusing a key for more accurate positioning and security. Referring toFIG. 4A, in an STS packet configuration 0 (zero), the PPDU may includeSHR, PHR, and PHY payload sequentially. Referring to FIG. 4B, in an STSpacket configuration 1 (one), the PPDU may include SHR, STS, PHR, andPHY payload sequentially. Referring to FIG. 4C, in an STS packetconfiguration 2 (two), the PPDU may include SHR, PHR, PHY payload, andSTS sequentially. Referring to FIG. 4D, in an STS packet configuration 3(three), the PPDU may include SHR, SFD, and STS sequentially. InHPRF-UWB, PHR and PHY payload may be modulated based on BPSK. As shownin FIGS. 4A to 4D, SHR of the HPRF-SHR may also include a SYNC field andan SFD field, and examples of symbols included in the SYNC field will bedescribed below with reference to FIG. 5 .

FIG. 5 is a diagram illustrating an example of a preamble symbolaccording to an embodiment, FIG. 6 is a diagram illustrating an exampleof a preamble code according to an embodiment, and FIGS. 7A and 7B arediagrams illustrating preamble parameters according to embodiments.

Referring to FIG. 5 , a preamble symbol S_(i) may be included in a SYNCfield of FIGS. 3 and 4A to 4D. For example, as described above withreference to FIG. 3 , the preamble symbol S_(i) may be repeated NSYNCtimes in the SYNC field. The preamble symbol S_(i) may be configured byspreading a preamble code C_(i) (which may be referred to as a code or acode sequence herein) having a code length L. The preamble code C_(i)may include L elements (i.e., C_(i)(0) C_(i)(L−1)), and each of the Lelements may be a ternary element having one of {-1, 0, 1} values.According to a code index i, the code length L of the preamble codeC_(i) and the values of elements may be defined. For example, as shownin FIG. 6 , the preamble code C_(i) of which code index i is 1 to 8 mayhave the code length L of 31, and may have different values according tochannel numbers. In some embodiments, although not shown in FIG. 6 , thepreamble code C_(i) of which code index i is 9 to 24 may have the codelength L of 127, and the preamble code C_(i) of which code index i is 25to 32 may have the code length L of 91.

Referring back to FIG. 5 , the preamble symbol S_(i) may include aplurality of chips. When δ_(L) is a delta length, a first chip amongδ_(L) consecutive chips in the preamble symbol S_(i) may have a value ofone element (e.g., C_(i)(0)) of the code C_(i), while subsequent(δ_(L)-1) chips may all have values of zero. The synchronizer 194 ofFIG. 2 may detect, based on the code C_(i), the SYNC field in which thesymbol S_(i) is NSYNC times repeated, and may identify the transmissionof a UWB packet frame.

As described above with reference to FIG. 2 , the synchronizer 194 mayreceive a series of input samples from the RX filter 192. In someembodiments, a sampling frequency of the input sample may correspond toa sampling frequency of the ADC 180, and the ADC 180 may over-sample ananalog signal. For example, as shown in FIG. 5 , in the series of inputsamples x, Lo consecutive input samples may be generated during aduration corresponding to one chip, and Lo may be referred to as anoversampling rate. As will be described below with reference to FIG. 9 ,in order to detect a symbol boundary, one input sample may be extractedfor each of δ_(L)Lo consecutive input samples among the series of inputsamples to calculate a correlation value.

Referring to FIGS. 7A and 7B, preambles of different configurations maybe used according to channel numbers. As shown in FIGS. 7A and 7B, thepreamble symbol S_(i) may include 496, 1984, 508, or 364 chips. Inaddition, the preamble symbol S_(i) may be configured based on thepreamble code C_(i) having the code length L of 31, 127, or 91, and thedelta length 6L may be 16, 64, or 4.

FIG. 8 is a flowchart illustrating a method for high-speedsynchronization according to an embodiment. Specifically, the flowchartof FIG. 8 shows the method for time synchronization. As shown in FIG. 8, the method for high-speed synchronization may include a plurality ofrounds of operations S10 to S60. In some embodiments, the method of FIG.8 may be performed by the synchronizer 194 of FIG. 2 . Hereinafter, FIG.8 will be described with reference to FIG. 2 .

Referring to FIG. 8 , correlation values may be calculated in a currentsymbol duration in operation S10. As described above with reference tothe drawings, the preamble symbol S_(i) may be generated based on thepreamble code C_(i) of the index i known in advance to a transmitter anda receiver, and the synchronizer 194 may detect a symbol boundary basedon a position corresponding to the highest correlation value amongcorrelation values between values extracted from the preamble symbolS_(i) and the preamble code C_(i). The correlation values may be complexnumbers, and an example of operation S10 will be described withreference to FIG. 9 .

In operation S20, phase differences between the correlation values of aprevious symbol duration and the correlation values of the currentsymbol duration are calculated. A carrier frequency offset may occur dueto a frequency deviation between an oscillator of the transmitter and anoscillator of the receiver, and accordingly, a phase difference mayoccur between a first correlation value (e.g., r^((m))(n) in FIG. 9 )calculated in the current symbol duration (e.g., S′_(m) in FIG. 9 ),i.e., a first symbol duration, and a second correlation value (e.g.,r^((m-1))(n) in FIG. 9 ) calculated in the previous symbol duration(e.g., S′_(m-1) in FIG. 9 ), i.e., a second symbol duration,corresponding to the same sample index (e.g., the sample index n in FIG.9 ). When the carrier frequency offset constantly increases ordecreases, the phase difference between the correlation value calculatedin the current symbol duration and the correlation value calculated inthe previous symbol duration, corresponding to the sample index of thesymbol boundary, may be constant. On the other hand, a phase differencebetween the correlation value calculated in the current symbol durationand the correlation value calculated in the previous symbol duration,corresponding to a sample index that is not the symbol boundary, mayvary. An example of operation S20 will be described below with referenceto FIG. 10 .

In operation S30, the accumulative phase differences may be updated.According to one embodiment, the accumulative phrase differencesrespectively corresponding to the input sample may be updated based onthe phase differences. For example, the synchronizer 194 may add thephase difference calculated in operation S20 to a current accumulativephase difference, and accordingly, accumulative phase differencesrespectively corresponding to sample indexes may be generated. Asdescribed above, the phase differences that correspond to the sampleboundary may have substantially constant values, and accordingly, theaccumulative phase difference that correspond to the sample boundary maygradually increase as the phase differences accumulate. On the otherhand, phase differences that do not correspond to the sample boundarymay vary, and accordingly, as the phase differences accumulate, theaccumulative phase differences that do not correspond to the sampleboundary may gradually decrease.

In operation S40, it is determined whether the accumulation of phasedifferences ends. For example, the synchronizer 194 may determinewhether phase differences have been accumulated with respect topreviously determined M symbols. As will be described below, operation40 may be performed using a modified integration method that overcomesthe limitations of both the coherent method and the non-coherent method.A non-coherent method may accumulate absolute values of correlationvalues respectively corresponding to a plurality of symbols in order todetect a symbol boundary, and a coherent method may directly accumulatethe correlation values. Because the accumulative phase differences maybe used to detect the symbol boundary, and accordingly, the symbolboundary may be detected with fewer symbols when using a coherent methodthan using a non-coherent method. According to an embodiment, thesynchronizer 194 may preset the number M of symbols for accumulatingphase differences to a relatively small value. As shown in FIG. 8 , whenthe continuation of accumulation is determined, i.e., the accumulationof phase difference does not end, the synchronizer 194 may move to anext symbol duration in operation S50, and may perform operations S10 toS30 again. On the other hand, when accumulation of phrase difference isdetermined to end, operation S50 might not be performed and operationS60 may be performed subsequently.

In operation S60, the symbol boundary may be detected. For example, thesynchronizer 194 may detect the symbol boundary based on theaccumulative phase differences respectively corresponding to the sampleindexes. Examples of operation S60 will be described below withreference to FIGS. 12 and 14 .

FIG. 9 is a diagram illustrating an operation of calculating correlationvalues according to an embodiment. As described above with reference toFIG. 8 , the synchronizer 194 of FIG. 2 may calculate correlation valuesin one symbol duration and may calculate phase differences between thecorrelation values respectively corresponding to adjacent symbols.According to an embodiment, phase differences between the correlationvalues of adjacent symbols accumulate and do not converge to zero.

Referring to FIG. 9 , a second correlation value r^((m-1))(n)corresponding to a second symbol duration S′_(m-1) may be calculated,and a first correlation value r^((m))(n) corresponding to a first symbolduration S′_(m) may be calculated. The input sample x(n) may refer to ann-th input sample in each of the symbol durations, the first correlationvalue r^((m))(n) may be calculated from input samples spaced apart fromeach other at equal intervals (i.e., a constant sample index difference)including the input sample x(n) in the first symbol duration S′_(m), andthe second correlation value r^((m-1))(n) may be calculated from inputsamples spaced apart from each other at equal intervals including theinput sample x(n) in the second symbol duration S′_(m-1). A correlationvalue (or a despreading value) r(n) corresponding to the input samplex(n) in one symbol duration may be calculated as in [Equation 1] below.

$\begin{matrix}\lbrack {{Equation}1} \rbrack &  \\{{r(n)} = \frac{\sum_{k = 0}^{L - 1}{{x( {n - {\delta_{L}L_{o}k}} )} \times {C_{i}(k)}}}{\sum_{k = 0}^{T_{sym} - 1}{❘{x(k)}❘}^{2}}} & (1)\end{matrix}$

In [Equation 1], Lo may be an oversampling rate according to a samplingrate of the ADC 180 of FIG. 2 , T_(sym) may be the number of inputsamples included in one symbol duration (T_(sym)=δ_(L)LOL), and C_(i)(k)may be a (k+1)-th value in the preamble code C_(i) having the code indexi (0≤k≤L−1).

The non-coherent method may accumulate absolute values of correlationvalues respectively corresponding to a plurality of symbols in order todetect a symbol boundary, and may detect an index of an input samplecorresponding to the maximum accumulative value as the symbol boundary.However, because the accumulated values respectively corresponding toinput samples independent of the symbol boundary may also increase dueto the use of absolute values of correlation values rather than a directuse of correlation values, the number of symbols that need to beconsidered for the symbol boundary may increase, and the time taken forsynchronization may be extended. A coherent method may directlyaccumulate the correlation values respectively corresponding to theplurality of symbols so as to detect the symbol boundary, and may detectthe index of the input sample corresponding to the maximum accumulativevalue as the symbol boundary. However, a conventional coherent methodmay also have its limitation in that a phase may gradually increase dueto the carrier frequency offset between the transmitter and thereceiver, and accordingly, an accumulated value converging to zeroaccording to the phase in the coherent method may occur. As describedabove, in the method of FIG. 8 , because the phase differences betweenthe correlation values of adjacent symbols accumulate, a problem of thecoherent method may be solved, and thus, synchronization may becompleted early and accurately.

FIG. 10 is a flowchart illustrating a method for high-speedsynchronization according to an embodiment. Specifically, the flowchartof FIG. 10 shows an example of operation S20 of FIG. 8 . As describedabove with reference to FIG. 8 , in operation S20′ of FIG. 10 , phasedifferences between correlation values of a current symbol duration andcorrelation values of a previous symbol duration may be calculated. Asshown in FIG. 10 , operation S20′ may include a plurality of rounds ofoperations S22, S24, and S26. In some embodiments, operation S20′ may beperformed by the synchronizer 194 of FIG. 2 , and FIG. 10 will bedescribed below with reference to FIGS. 2 and 9 .

Referring to FIG. 10 , a pair of correlation values corresponding to thesame sample index may be obtained in operation S22. For example, thesynchronizer 194 may calculate the first correlation value r^(m)(n) ofthe first symbol duration S′_(m), and may read the second correlationvalue r^((m-1))(n) of the second symbol duration S′_(m-1) from a bufferconfigured to store second correlation values (e.g., BUF2 in FIGS. 16Aand 16B).

In operation S24, a complex conjugate number of the correlation value ofthe previous symbol duration may be calculated, and in operation S26,the correlation value of the current symbol duration may be multipliedby the complex conjugate number. For example, the synchronizer 194 maycalculate a complex conjugate of the second correlation valuer^((m-1))(n), and may multiply a complex conjugate number of the secondcorrelation value r^((m-1))(n) by the first correlation value r^(m)(n).That is, a phase difference p_(d) ^((m))(n) between the firstcorrelation value r^((m))(n) and the second correlation valuer^((m-1))(n) may be calculated as in Equation (2) below:

p _(d) ^((m))(n)=r ^(m)(n)×conj(r ^((m-1))(n))  (2)

In Equation (2), p_(d) ^((m))(n) may mean a phase difference betweenvalues despreaded from adjacent symbols, and may be a complex number.

FIG. 11 is a flowchart illustrating a method for high-speedsynchronization according to an embodiment. Specifically, the flowchartof FIG. 11 shows an example of operation S30 of FIG. 8 . As describedabove with reference to FIG. 8 , accumulative phase differences may beupdated in operation S30′ of FIG. 11 . In some cases, the accumulativephase differences are updated to respectively correspond to the inputsamples based on the phase differences. The updated accumulative phasedifferences may be used to perform simultaneous time and frequencysynchronization. In some cases, a wireless signal may be processed basedon the simultaneous time and frequency synchronization. According to anembodiment, the simultaneous time and frequency synchronization may beperformed based on a pre-determined preamble code. As shown in FIG. 11 ,operation S30′ may include a plurality of rounds of operations S32, S34,S36, and S38. In some embodiments, operation S30′ may be performed bythe synchronizer 194 of FIG. 2 , and FIG. 11 will be described belowwith reference to FIG. 2 .

Referring to FIG. 11 , in operation S32, it may be determined whether acurrent symbol duration is an initial symbol duration. For example, thesynchronizer 194 may determine whether the current symbol duration isthe initial symbol duration among M symbol durations. As shown in FIG.11 , when the current symbol duration is the initial symbol duration,the accumulative phase difference may be set to zero in operation S38,and operation S30′ may end. On the other hand, when the current symbolduration is not the initial symbol duration, that is, when a symbolduration preceding the current symbol duration exists, operations S34and S36 may be performed subsequently.

In operation S34, a phase difference and the accumulative phasedifference corresponding to the same sample index may be obtained. Forexample, the synchronizer 194 may obtain the phase difference calculatedin operation S20 of FIG. 8 , and read the already calculatedaccumulative phase difference from the buffer configured to storeaccumulative phase difference corresponding to the input samples (e.g.,BUF3 of FIGS. 16A and 16B).

In operation S36, the phase difference and the accumulative phasedifference may be summed. For example, the synchronizer 194 may updatethe accumulative phase difference by adding the phase differenceobtained in operation S34 to the accumulative phase difference. Twophase differences p_(d) ^((m))(n) and p_(d) ^((k))(n) may be expressedby Euler's formula as Equation (3) below.

p _(d) ^((m))(n)=r _(m)(cos θ_(m) +j sin θ_(m))  (3)

p _(d) ^((k))(n)=r _(k)(cos θ_(k) +j sin θ_(k))

When r_(m) and r_(k) are approximately equal to each other, i.e., thedifference between r_(m) and r_(k) is less than a pre-determinedthreshold value, the accumulative phase difference may be obtained byadding the two phase differences p_(d) ^((m))(n) (n) and p_(d)^((k))(n), and may be calculated as Equation (4).

$\begin{matrix}{{{p_{d}^{(m)}(n)} + {p_{d}^{(k)}(n)}} = {{{{r_{m}( {{\cos\theta_{m}} + {js{in}\theta_{m}}} )} + {r_{k}( {{\cos\theta_{k}} + {j\sin\theta_{k}}} )}} \cong {2 \cdot {\cos( \frac{\theta_{m} - \theta_{k}}{2} )} \cdot {r_{m}( {{\cos( \frac{\theta_{m} + \theta_{k}}{2} )} + {js{{in}( \frac{\theta_{m} + \theta_{k}}{2} )}}} )}}} = {{2 \cdot {\cos( \frac{\theta_{m} - \theta_{k}}{2} )} \cdot r_{m}}e^{\frac{\theta_{m} + \theta_{k}}{2}}}}} & (4)\end{matrix}$

Accordingly, as shown in Equation (5) below, a phase of the sum of thetwo phase differences p_(d) ^((m))(n) and p_(d) ^((k))(n) may be equalto an average phase difference of the two phase differences p_(d)^((m))(n) and p_(d) ^((k))(n).

$\begin{matrix}{{< ( {{p_{d}^{(m)}(n)} + {p_{d}^{(k)}(n)}} )} = \frac{\theta_{m} + \theta_{k}}{2}} & (5)\end{matrix}$

As described above with reference to FIG. 8 , when a carrier frequencyoffset increases or decreases with a constant inclination, θ_(m) andθ_(k) of Equation (5) may be approximately equal to each other, and thesum of the phase differences may be calculated as Equation (6) below.

p _(d) ^((m))(n)+p _(d) ^((k))(n)≅2·r _(m) e ^(θ) ^(m)   (6)

Accordingly, as phase differences accumulate at a symbol boundary, theaccumulative phase difference may increase, and the symbol boundary maybe detected based on the accumulative phase difference. An accumulativephase difference p_(d) ^((m)) updated in an m-th symbol duration may beexpressed as in Equation (7) below.

$\begin{matrix}{{P_{d}^{(m)}(n)} = \{ \begin{matrix}{{0{if}m} = 0} \\{{P_{d}^{({m - 1})} + {p_{d}^{(m)}(n)}} = {\sum\limits_{i = 1}^{m}{{r^{(i)}(n)} \times {{conj}( {r^{({i - 1})}(n)} )}{otherwise}}}}\end{matrix} } & (7)\end{matrix}$

FIG. 12 is a flowchart illustrating a method for high-speedsynchronization according to an embodiment. Specifically, the flowchartof FIG. 12 shows an example of operation S60 of FIG. 8. As describedabove with reference to FIG. 8 , a symbol boundary may be detected inoperation S60′ of FIG. 12 . As shown in FIG. 12 , operation S60′ mayinclude a plurality of rounds of operations S61 to S65. In someembodiments, operation S60′ may be performed by the synchronizer 194 ofFIG. 2 , and FIG. 12 will be described below with reference to FIG. 2 .

Referring to FIG. 12 , accumulative correlation values may be updated inoperation S61. For example, the synchronizer 194 may accumulatecorrelation values calculated in M symbol durations based on anaccumulative phase difference. Accordingly, a problem of a coherentmethod of simply accumulating correlation values may be solved. Anexample of operation S61 will be described below with reference to FIG.13 .

In operation S62, the maximum value of the updated accumulativecorrelation values may be identified. For example, the synchronizer 194may calculate T_(sym) accumulative correlation values over M symboldurations, and may identify the maximum value among the T_(sym)accumulative correlation values. As described above, the correlationvalues may be accumulated based on the accumulative phase difference inoperation S61, and accordingly, the maximum value of the accumulativecorrelation values may indicate a symbol boundary.

In operation S63, the maximum value may be compared with a firstreference value T_(c). For example, the synchronizer 194 may compare themaximum value identified in operation S62 with the first reference valueT_(c). When the maximum value identified in operation S62 is small, anerroneous symbol boundary is detected or that there is no symbolboundary. Accordingly, the synchronizer 194 may determine that a maximumvalue greater than or equal to the first reference value T_(c) is valid,while determining that a maximum value less than the first referencevalue T_(c) is invalid. As shown in FIG. 12 , when the maximum value isless than the first reference value T_(c), it may be determined inoperation S64 that the symbol boundary is undetectable. In someembodiments, when it is determined that the symbol boundary isundetectable, the method of FIG. 8 may be performed again. On the otherhand, when the maximum value is equal to or greater than the firstreference value T_(c), operation S65 may be subsequently performed.

In operation S65, a sample index corresponding to the maximum value maybe identified. For example, when accumulative correlation valuesaccumulated over M symbol durations are r ^((M))(n), the synchronizer194 may identify the sample index n_(s) that satisfies Equation (8)below.

$\begin{matrix}{n_{s} = {\arg\max\limits_{{n \in {\lbrack{0,T_{sym}}}})}{❘{{\overset{\_}{r}}^{(M)}(n)}❘}}} & (8)\end{matrix}$

Also, as described above, an accumulative correlation value r^((M))(n_(s)) of the sample index n_(s) may satisfy Equation (9) below.

| r ^((M))(n _(s))>T _(c)  (9)

In some embodiments, when the RX antenna 160 of FIG. 2 includes aplurality of (10) antennas, a symbol boundary may be detected fromaccumulative correlation values respectively calculated from theplurality of antennas. For example, when the accumulative correlationvalue of an antenna of index i among the total I antennas is r _(i)^((M))(n), the synchronizer 194 may identify the sample index n_(s)satisfying Equation (10) below.

$n_{s} = {\arg\max\limits_{{n \in {\lbrack{0,T_{sym}}}})}{\sum_{i = 0}^{I}{❘{{\overset{\_}{r}}_{i}^{(M)}(n)}❘}}}$

In addition, the sum of the accumulative correlation values for eachantenna of the sample index n_(s) may satisfy Equation (11) below.

$\begin{matrix}{{❘{\sum\limits_{i = 0}^{I}{❘{{\overset{\_}{r}}_{i}^{(M)}(n)}❘}}❘} > T_{c}} & (11)\end{matrix}$

FIG. 13 is a flowchart illustrating a method for high-speedsynchronization according to an embodiment. Specifically, the flowchartof FIG. 13 shows an example of operation S61 of FIG. 12 . As describedabove with reference to FIG. 12 , accumulative correlation values may beupdated in operation S61′ of FIG. 13 . As shown in FIG. 13 , operationS61′ may include a plurality of rounds of operations S61_2, S61_4, andS61_6. In some embodiments, operation S61′ of FIG. 13 may be performedby the synchronizer 194 of FIG. 2 , and FIG. 13 will be described belowwith reference to FIG. 2 .

Referring to FIG. 13 , an accumulative correlation value may be obtainedin operation S61_2. For example, the synchronizer 94 may read theaccumulative correlation value from a buffer configured to storeaccumulative correlation values (e.g., BUF4 in FIG. 16A). The readaccumulative correlation value may correspond to correlation valuesaccumulated up to a previous symbol duration.

In operation S61_4, the accumulative correlation value may be correctedbased on an accumulative phase difference. For example, the synchronizer194 may shift a phase of the accumulative correlation value obtained inoperation S61_2, based on the accumulative phase difference.Accordingly, an accumulative correlation value of which phase differenceis compensated for, that is, the corrected accumulative correlationvalue, may be generated.

In operation S61_6, the correlation value of the current symbol durationand the corrected accumulative correlation value may be summed. Forexample, the synchronizer 194 may generate an updated accumulativecorrelation value by adding the accumulative correlation value correctedin operation S61_4 to the correlation value of the current symbolduration. The accumulative correlation value r ^((m))(n) of the firstsymbol duration S′_(m) may be calculated from the accumulativecorrelation value r ^((m-1))(n) of the second symbol duration S′_(m-1)and the updated accumulative phase difference P_(d) ^((m))(n) as inEquation (12) below.

$\begin{matrix}{{{\overset{\_}{r}}^{(m)}(n)} = {{r^{(m)}(n)} + {{{\overset{\_}{r}}^{({m - 1})}(n)}e^{j < {P_{d}^{(m)}(n)}}}}} & (12)\end{matrix}$

The second term on the right side of Equation (12), i.e.,

${{{\overset{\_}{r}}^{({m - 1})}(n)}e^{j < {P_{d}^{(m)}(n)}}},$

may correspond to the accumulative correlation value corrected inoperation S61_4.

FIG. 14 is a flowchart illustrating a method for high-speedsynchronization according to an embodiment. Specifically, the flowchartof FIG. 14 shows an example of operation S60 of FIG. 8 . As describedabove with reference to FIG. 8 , a symbol boundary may be detected inoperation S60″ of FIG. 13 . As shown in FIG. 14 , operation S60″ mayinclude a plurality of operations S66 to S69. In some embodiments,operation S60″ may be performed by the synchronizer 194 of FIG. 2 , andFIG. 14 will be described below with reference to FIG. 2 .

Referring to FIG. 14 , a maximum value among accumulative phasedifferences may be identified in operation S66. As described above withreference to the drawings, the maximum value of accumulative phasedifferences as well as a maximum value of accumulative correlationvalues may occur at a symbol boundary. Accordingly, instead ofcalculating the accumulative correlation value based on the accumulativephase difference, the symbol boundary may be directly detected fromaccumulative phase differences. For example, the synchronizer 194 mayidentify the maximum value among accumulative phase differencesaccumulated in M symbol durations.

In operation S67, the maximum value may be compared with a secondreference value T_(d). For example, the synchronizer 194 may compare themaximum value identified in operation S66 with the second referencevalue T_(d). When the maximum value identified in operation S66 issmall, an erroneous symbol boundary is detected or that there is nosymbol boundary. Accordingly, the synchronizer 194 may determine thatthe maximum value equal to or greater than the second reference valueT_(d) is valid, while determining that the maximum value less than thesecond reference value T_(d) is invalid. As shown in FIG. 14 , when themaximum value is less than the second reference value T_(d), it may bedetermined that the symbol boundary is undetectable in operation 568. Insome embodiments, when it is determined that the symbol boundary isundetectable, the method of FIG. 8 may be performed again. On the otherhand, when the maximum value is equal to or greater than the secondreference value T_(d), operation S69 may be subsequently performed.

In operation S69, a sample index corresponding to the maximum value maybe identified.

For example, the synchronizer 194 may identify the sample index n_(s)that satisfies Equation (13) below.

$\begin{matrix}{n_{s} = {\arg\max\limits_{{n \in {\lbrack{0,T_{sym}}}})}{❘{P_{d}^{(M)}(n)}❘}}} & (13)\end{matrix}$

Also, as described above, the accumulative phase difference P_(d)^((M))(n) of the sample index n_(s) may satisfy Equation (14) below.

|P _(d) ^((M))(n)|>T _(d)  (14)

In some embodiments, when the RX antenna 160 of FIG. 2 includes aplurality of antennas, the symbol boundary may be detected fromaccumulative phase differences respectively calculated from theplurality of antennas. For example, when an accumulative phasedifference of the antenna of the index i among the total I antennas isP_(i,d) ^((M))(n), the synchronizer 194 may identify the sample indexn_(s) that satisfies Equation (15) below.

$\begin{matrix}{n_{s} = {\arg\max\limits_{{n \in {\lbrack{0,T_{sym}}}})}{\sum\limits_{i = 0}^{I}{P_{i,d}^{(M)}(n)}}}} & (15)\end{matrix}$

In addition, the sum of the accumulative phase differences for eachantenna of the sample index n_(s) may satisfy Equation (16) below.

$\begin{matrix}{{❘{\sum\limits_{i = 0}^{I}{❘{P_{i,d}^{(M)}(n)}❘}}❘} > T_{d}} & (16)\end{matrix}$

FIG. 15 is a flowchart illustrating a method for high-speedsynchronization according to an embodiment. Specifically, FIG. 15 showsa method for frequency synchronization. As shown in FIG. 15 , the methodfor high-speed synchronization may include a plurality of rounds ofoperations S72, S74, S82, and S84. In some embodiments, the method ofFIG. 15 may be performed after operation S60 of FIG. 8 is performed, andmay use the sample index n_(s) corresponding to a symbol boundary. Insome embodiments, the method of FIG. 15 may be performed by thesynchronizer 194 of FIG. 2 . Hereinafter, FIG. 15 will be described withreference to FIG. 2 .

Referring to FIG. 15 , a phase corresponding to an index identified inoperation S72 may be identified, and an initial phase may be determinedin operation S74. For example, the synchronizer 194 may identify a phaseof a correlation value r^((m-1))(n_(s)) corresponding to the sampleindex n_(s), and determine the phase of the correlation valuer^((m-1))(n_(s)) to be the initial phase. The synchronizer 194 mayprovide information about the initial phase to the RX filter 192.

An accumulative phase difference corresponding to a sample index may beidentified in operation S82, and a carrier frequency offset may becalculated in operation S84. For example, the synchronizer 194 mayidentify an accumulative phase difference P_(d) ^((M))(n_(s))corresponding to the sample index n_(s), and calculate a carrierfrequency offset based on a phase of the accumulative phase differenceP_(d) ^((M))(n_(s)). The carrier frequency offset {circumflex over(F)}_(init_offset) may be calculated as in Equation (17) below.

$\begin{matrix}{{\hat{F}}_{{init}\_{offset}} = {\frac{< {P_{d}^{(M)}( n_{s} )}}{T_{sym}} \cong \frac{\theta_{f_{o}}^{(M)}( n_{s} )}{T_{sym}}}} & (17)\end{matrix}$

In Equation (17), θ_(fo) ^((M))(n_(s)) may mean a phase change due tothe carrier frequency offset.

FIGS. 16A and 16B are block diagrams illustrating examples ofsynchronizers 200 a and 200 b respectively according to embodiments.Specifically, the block diagram of FIG. 16A shows the synchronizer 200 aperforming operation S60′ of FIG. 12 , and the block diagram of FIG. 16Bshows the synchronizer 200 b performing operation S60″ of FIG. 14 .

Referring to FIG. 16A, the synchronizer 200 a may include first tofourth buffers BUF1 to BUF4 and a processing circuit PRO. The processingcircuit PRO may store data in the first to fourth buffers BUF1 to BUF4and read data stored in the first to fourth buffers BUF1 to BUF4. Thefirst to fourth buffers BUF1 to BUF4 may have a structure capable ofstoring data. In some embodiments, the first to fourth buffers BUF1 toBUF4 may correspond to regions of a memory device, and the processingcircuit PRO may access the first to fourth buffers BUF1 to BUF4 throughan address. In some embodiments, the first to fourth buffers BUF1 toBUF4 may include registers dedicated to the processing circuit PRO. Themodules included in the processing circuit PRO in FIGS. 16A and 16B maycorrespond to an independent circuit, a software block (procedure orsubroutine) executed by a processor, or a combination thereof.

The processing circuit PRO may include first to tenth modules 201 a to210 a. The input sample x may be stored in the first buffer BUF1. Forexample, the first buffer BUF1 may store input samples corresponding toone symbol duration. As described above with reference to FIG. 9 , thefirst module 201 a may read the n-th input sample and the input samplesspaced apart from each other by an interval corresponding to δ_(L) chipsof delta length, i.e., δ_(L)Lo indexes, from the first buffer BUF1, andcalculate a correlation value r^((m))(n) based on the read input samplesand a preamble code. As shown in FIG. 16A, the correlation valuer^((m))(n) may be stored in the second buffer BUF2. According to anembodiment, the first module 201 a may calculate a plurality ofcorrelation values respectively corresponding to a plurality of readinput samples.

The second module 202 a may read a correlation value r^((m-1))(n)corresponding to the n-th input sample in a previous symbol durationfrom the second buffer BUF2, and provide a complex conjugate of thecorrelation value r^((m-1))(n) to the third module 203 a. The thirdmodule 203 a may multiply the correlation value r^((m))(n) of thecurrent symbol duration by the complex conjugate of the correlationvalue r^((m-1))(n) of the previous symbol duration, and generate thephase difference p_(d) ^((m))(n). The fourth module 204 a may read anaccumulative phase difference p_(d) ^((m-1))(n) calculated up to theprevious symbol duration from the third buffer BUF3. The fourth module204 a may sum the phase difference p_(d) ^((m))(n) calculated in thecurrent symbol duration by the third module 203 a and the accumulativephase difference p_(d) ^((m-1))(n) read from the third buffer BUF3,generate an accumulative phase difference P_(d) ^((m))(n), and store theaccumulative phase difference P_(d) ^((m))(n) in the third buffer BUF3.

The fifth module 205 a may receive the accumulative phase differenceP_(d) ^((m))(n) from the fourth module 204 a, and provide the phase ofthe accumulative phase difference P_(d) ^((m))(n) to the sixth module206 a. The sixth module 206 a may read an accumulative correlation valuer ^((m-1))(n) calculated up to the previous symbol duration from thefourth buffer BUF4, and provide the accumulative correlation value r^((m-1))(n) shifted by the phase provided from the fifth module 205 a tothe seventh module 207 a. The seventh module 207 a may sum thecorrelation value r^((m))(n) of the current symbol duration and thecorrected accumulative correlation value provided from the sixth module206 a, and generate an accumulative correlation value r ^((m))(n). Asshown in FIG. 16A, the seventh module 207 a may store the accumulativecorrelation value r ^((m))(n) in the fourth buffer BUF4.

When operations of the first to seventh modules 201 a to 207 a arecompleted on M symbol durations, the second buffer BUF2 may storeT_(sym) correlation values {r^((M))(n)|0≤n≤T_(sym)−1}, the third bufferBUF3 may store T_(sym) accumulative phase differences {P_(d)^((M))(n)|0≤n≤T_(sym)−1}, and the fourth buffer BUF4 may store T_(sym)accumulative correlation values {r ^((M))(n)|0≤n≤T_(sym)−1}.

The eighth module 208 a may read the accumulative correlation value r^((M)) (n) from the fourth buffer BUF4, and provide an absolute value |r^((M))(n)| of the accumulative correlation value r ^((M)) (n) to theninth module 209 a. The ninth module 209 a may identify a maximum valueamong absolute values provided from the eighth module 208 a, and mayprovide the identified maximum value to the tenth module 210 a. Thetenth module 210 a may compare the maximum value provided from the ninthmodule 209 a with the first reference value T_(c), and when the maximumvalue is equal to or greater than the first reference value T_(c),output an activated signal LOCK indicating completion ofsynchronization.

As shown in FIG. 16A, the ninth module 209 a may identify the sampleindex n_(s) corresponding to the maximum value. As indicated by a dashedarrow in FIG. 16A, a correlation value r^((M))(n_(s)) corresponding tothe sample index n_(s) may be read among correlation values stored inthe second buffer BUF2, and the phase of the correlation valuer^((M))(n_(s)) may be determined as an initial phase. Also, as indicatedby a dashed arrow in FIG. 16A, an accumulative phase difference P_(d)^((M))(n_(s)) corresponding to the sample index n_(s) among thecorrelation values stored in the third buffer BUF3 may be read from thethird buffer BUF3, and a carrier frequency offset may be calculatedbased on the phase of the accumulative phase difference P_(d)^((M))(n_(s)).

Referring to FIG. 16B, the synchronizer 200 b may include the first tothird buffers BUF1 to BUF3 and the processing circuit PRO. In someexamples, compared with the synchronizer 200 a of FIG. 16A, the fourthbuffer BUF4 might not be included in the synchronizer 200 b of FIG. 16B.The processing circuit PRO may include first to seventh modules 201 b to207 b. The first to fourth modules 201 b to 204 b may operate in thesame manner as the first to fourth modules 201 a to 204 a of FIG. 16A.

The fifth module 205 b may read the accumulative phase differenceP_(d)(M)(n) from the third buffer BUF3, and provide an absolute value|P_(d) ^((M))(n)| of the accumulative phase difference P_(d) ^((M))(n)to the sixth module 206 b. The sixth module 206 b may identify a maximumvalue among absolute values provided from the fifth module 205 b, andmay provide the identified maximum value to the seventh module 207 b.The seventh module 207 b may compare the maximum value provided from thesixth module 206 b with the second reference value T_(d), and when themaximum value is equal to or greater than the second reference valueT_(d), output the activated signal LOCK indicating completion ofsynchronization.

FIG. 17 is a block diagram illustrating a synchronizer 300 according toan embodiment. As shown in FIG. 17 , the synchronizer 300 may include atleast one processor 310 and a memory 320. The at least one processor 310may access the memory 320, and the memory 320 may include a series ofinstructions INST and the first to fourth buffers BUF1 to BUF4. In someembodiments, as described above with reference to FIG. 16B, the fourthbuffer BUF4 may be omitted from the memory 320.

In some embodiments, at least part of the method for high-speedsynchronization described above with reference to the drawings may beperformed by the at least one processor 310 executing the series ofinstructions INST stored in the memory 320. For example, the at leastone processor 310 may perform at least one of operations of FIG. 8 andat least one of operations of FIG. 15 , by executing the series ofinstructions INST. In some embodiments, the at least one processor 310may include a cache memory, and may store data read from the memory 320in the cache memory or write data stored in the cache memory into thememory 320.

The memory 320 may have any structure accessible by the at least oneprocessor 310. For example, the memory 320 may include a volatile memorydevice, such as dynamic random access memory (DRAM) and static randomaccess memory (SRAM), or a non-volatile memory device, such as flashmemory. In some embodiments, the memory 320 may include two or morememory devices, and the series of instructions INST and the first tofourth buffers BUF1 to BUF4 may be stored in the two or more memorydevices. For example, the series of instructions INST may be stored in afirst memory device, and the first to fourth buffers BUF1 to BUF4 may beimplemented in a second memory device.

While the present disclosure has been particularly shown and describedwith reference to embodiments thereof, it will be understood thatvarious changes in form and details may be made therein withoutdeparting from the spirit and scope of the following claims.

1. A method comprising: calculating first correlation valuescorresponding to a first symbol duration based on input samples, theinput samples being generated from a received signal; calculating phasedifferences respectively corresponding to the input samples based on thefirst correlation values and second correlation values corresponding toa second symbol duration preceding the first symbol duration; updatingaccumulative phase differences respectively corresponding to the inputsamples based on the phase differences; and detecting a symbol boundarybased on the updated accumulative phase differences.
 2. The method ofclaim 1, wherein the first correlation values and the second correlationvalues are complex numbers, wherein calculating the phase differencescomprises: obtaining a first correlation value from the firstcorrelation values and a second correlation value from the secondcorrelation values, the first correlation value and the secondcorrelation value corresponding to a same index of an input sample;calculating a complex conjugate of the obtained second correlationvalue; and multiplying the obtained first correlation value by thecalculated complex conjugate of the obtained second correlation value.3. The method of claim 1, wherein the phase differences and theaccumulative phase differences are complex numbers, wherein updating theaccumulative phase differences comprises: obtaining a phase differencefrom the phase differences and an accumulative phase difference from theaccumulative phase differences, the phase difference and theaccumulative phase difference corresponding to a same index of an inputsample; and summing the obtained phase difference and the obtainedaccumulative phase difference.
 4. The method of claim 3, whereinupdating the accumulative phase differences further comprises settingthe accumulative phase difference to zero when the first symbol durationis an initial symbol duration.
 5. The method of claim 1, whereindetecting the symbol boundary comprises: updating accumulativecorrelation values based on the first correlation values and the updatedaccumulative phase differences; identifying a maximum value among theupdated accumulative correlation values; and determining an index of aninput sample corresponding to the maximum value.
 6. The method of claim5, wherein updating the accumulative phase differences furthercomprises: correcting the accumulative correlation value based on theupdated accumulative phase difference; and summing the first correlationvalue and the corrected accumulative correlation value.
 7. The method ofclaim 5, wherein detecting the symbol boundary further comprises:comparing the maximum value with a first reference value; and when themaximum value is less than the first reference value, determining thatthe symbol boundary is undetectable.
 8. The method of claim 1, whereinthe detecting of the symbol boundary further comprises: identifying amaximum value among the updated accumulative phase differences; anddetermining an index of an input sample corresponding to the maximumvalue.
 9. The method of claim 8, wherein detecting the symbol boundaryfurther comprises: comparing the maximum value with a second referencevalue; and when the maximum value is less than the second referencevalue, determining that the symbol boundary is undetectable. 10.(canceled)
 11. (canceled)
 12. The method of claim 1, wherein each of thefirst symbol duration and the second symbol duration corresponds to aduration of a single symbol included in a SYNC field included in asynchronization header (SHR).
 13. An apparatus comprising: a firstbuffer configured to store input samples generated from a receivedsignal and corresponding to a first symbol duration; a processingcircuit configured to calculate first correlation values respectivelycorresponding to the input samples based on the input samples; a secondbuffer configured to store second correlation values corresponding to asecond symbol duration preceding the first symbol duration; and a thirdbuffer configured to store accumulative phase differences respectivelycorresponding to the input samples, wherein the processing circuit isfurther configured to: calculate phase differences respectivelycorresponding to the input samples, based on the first correlationvalues and the second correlation values; update the accumulative phasedifferences based on the phase differences; and detect a symbol boundarybased on the updated accumulative phase differences.
 14. The apparatusof claim 13, wherein the first correlation values and the secondcorrelation values are complex numbers, wherein the processing circuitis further configured to read a second correlation value from the secondbuffer, the second correlation value corresponding to a same index of aninput sample corresponding to a first correlation value; and calculatethe phase differences by multiplying the first correlation value by acomplex conjugate of the read second correlation value.
 15. Theapparatus of claim 13, wherein the phase differences and theaccumulative phase differences are complex numbers, wherein theprocessing circuit is further configured to read an accumulative phasedifference from the third buffer, the accumulative phase differencecorresponding to a same index of an input sample corresponding to one ofthe phase differences; and update the accumulative phase differences bysumming the one of the phase differences and the read accumulative phasedifference.
 16. The apparatus of claim 15, wherein the processingcircuit is further configured to set the accumulative phase differenceto zero when the first symbol duration is an initial symbol duration.17. The apparatus of claim 13, wherein the processing circuit is furtherconfigured to update accumulative correlation values based on the firstcorrelation values and the updated accumulative phase differences;identify a maximum value among the updated accumulative correlationvalues; and determine an index of an input sample corresponding to themaximum value.
 18. The apparatus of claim 17, further comprising: afourth buffer configured to store accumulative correlation values,wherein the processing circuit is further configured to read theaccumulative correlation value from the fourth buffer; correct the readaccumulative correlation value based on the updated accumulative phasedifference; and update the accumulative correlation values by summingthe first correlation value and the corrected accumulative correlationvalue.
 19. (canceled)
 20. The apparatus of claim 13, wherein theprocessing circuit is further configured to determine an index of asample input corresponding to a maximum value of the updatedaccumulative phase differences.
 21. (canceled)
 22. The apparatus ofclaim 13, wherein the processing circuit is further configured toidentify a phase of a first correlation value corresponding to thedetected symbol boundary, and determine the identified phase to be aninitial phase.
 23. The apparatus of claim 13, wherein the processingcircuit is further configured to calculate a carrier frequency offsetbased on the first symbol duration and an accumulative phase differencecorresponding to the detected symbol boundary.
 24. (canceled)
 25. Anapparatus comprising: a memory storing a series of instructions; and atleast one processor configured to, by executing the series ofinstructions, calculate first correlation values corresponding to afirst symbol duration and respectively corresponding to input samples,the input samples being generated from a received signal; calculatephase differences respectively corresponding to the input samples, basedon the first correlation values and second correlation valuescorresponding to a second symbol duration preceding the first symbolduration; update accumulative phase differences respectivelycorresponding to the input samples based on the phase differences; anddetect a symbol boundary based on the updated accumulative phasedifferences.
 26. (canceled)
 27. (canceled)